Triassic stratigraphy, paleontology and correlation, south-central New Mexico
Spencer G. Lucas
Triassic strata in south-central New Mexico (Valencia, Socorro and Lincoln Counties) pertain to the Moenkopi, Shinarump, Santa Rosa and San Pedro Arroyo Formations. The Moenkopi Formation is as much as 102 m thick, is dominated by grayish red, trough-crossbedded litharenite and rests disconformably on Permian strata of the Artesia Formation. As much as 5 m of pedogenically modified, color-mottled sandstone, siltstone and conglomerate above Moenkopi strata in parts of south-central New Mexico are identified informally as the mottled strata. The Shinarump Formation (Valencia and Socorro Counties) and Santa Rosa Formation (Lincoln County) of the Chinle Group overlie the Moenkopi Formation or mottled strata. The Shinarump is as much as 6 m of trough-crossbedded, silica-pebble conglomerate, whereas the Santa Rosa is 13-26 m of silica-pebble conglomerate and micaceous subarkose. The mudstone-dominated Upper Triassic strata in south-central New Mexico above the Shinarump and Santa Rosa are here named the San Pedro Arroyo Formation, which includes as much as 123 m of variegated, bentonitic mudstone and minor conglomerate, sandstone, siltstone and limestone. A distinctive, limestone-dominated interval in the lower part of the San Pedro Arroyo Formation is here named the Ojo Huelos Member. Sparse paleontological evidence supports an Anisian age for the Moenkopi Formation in south-central New Mexico and indicates a late Carnian age for the lower part of the San Pedro Arroyo Formation (including the Ojo Huelos Member). The upper part of the San Pedro Arroyo Formation is Late Triassic, but a more precise age cannot be determined from available data. Fossils, lithology and stratigraphic sequence allow correlation of the Triassic strata in south-central New Mexico with Triassic strata elsewhere in the state.
- Lucas, Spencer G., 1991, Triassic stratigraphy, paleontology and correlation, south-central New Mexico, in: Geology of the Sierra Blanca, Sacramento and Capitan Ranges, New Mexico, Barker, James M.; Kues, Barry S.; Austin, George S.; Lucas, Spencer, G., New Mexico Geological Society, Guidebook, 42nd Field Conference, pp. 243-259.